1. Field of the Invention
The present invention relates to a device for controlling a cooling system of an internal combustion engine and a method for controlling the cooling system of the internal combustion engine in which a circulation passage for a coolant is defined in an internal combustion engine such as an automobile engine or the like and more particularly to a device and a method for controlling a device and a method for controlling the temperature of the coolant to be circulated within the internal combustion engine to remain in an optimum state.
2. Description of the Related Art
In an automobile internal combustion engine (hereinafter referred to as the "engine "), a water cooled type cooling system in which a radiator is provided for cooling the engine is generally used.
In a cooling system of this kind, there is used a thermostat employing a thermal expansion body for controlling the volume of cooling water circulated to the radiator side for controlling the temperature of the cooling water to be introduced into the engine, or a valve unit for controlling the same electrically.
FIG. 13 shows one example of a cooling device using an electrically controlled valve unit.
The numeral 1 denotes an engine composed of a cylinder block 1a and a cylinder head 1b which define circulation passages therewithin as shown by arrows c.
The numeral 2 denotes a heat exchanger or a radiator which is formed with a known fluid passage 2c, radiator 2 being further formed with a cooling water inlet 2a and a cooling water outlet 2b. Radiator 2 is connected to the engine 1 via a cooling water passage 3 which circulates the cooling water.
The cooling water passage 3 is composed of an outlet side cooling water passage 3a communicating the cooling water outlet 1d provided in the upper portion of the engine with the cooling water inlet 2a provided in the upper portion of said radiator 2, an inlet side cooling water path 3b communicating the cooling water outlet 2b provided in the lower portion of the radiator with the cooling water inlet 1e provided in the lower portion of the engine 1, and a bypass 3c forming an intermediate portions of said cooling water passages 3a and 3b.
Combination of all of said engine 1, radiator 2 and the cooling water passage 3 completes a circulation passage 4 of the coolant. Then, an electrically controlled valve unit 5 is connected to the inlet side cooling water passage 3a between a branch- off portion of the bypass 3c and the cooling water inlet 2a of the radiator 2.
A butterfly valve or the like is used for said valve unit 5, which is operated to open and close through forward and reverse rotations of an electric motor or the like (not shown) installed in the valve unit such that the volume of the flow of the cooling water to be supplied to the radiator 2 is controlled.
On the other hand, there is provided a temperature detecting element 6 in the form of a thermister or the like at the connection of the inlet side cooling water passage 3b and the bypass 3c. Values detected by said temperature detecting element 6 are converted by a converter 7 into data recognizable by an engine control unit 8 (hereinafter referred to as ECU) so as to be supplied to said ECU 8 which controls the overall operation of the engine.
From said ECU 8, there are supplied control signals obtained on basis of the values of the temperatures of the cooling water detected by the temperature detecting elements 6 to a motor control circuit 9, which is constructed such that a drive current is supplied to the motor provided in the valve unit 5 from a battery 10 by the control signals from the ECU 8.
Further, FIG. 13 shows a water pump 11 provided at the inlet portion 1e of the engine 1 such that the cooling water is forced to be circulated by the revolution of a crankshaft (not shown) of the engine 1. Further, the numeral 12 denotes a fan unit for forcibly introducing a cooling air to the radiator 2, said fan unit 12 being composed of the cooling fan 12a and the motor 12b for driving the same.
In a construction described in the foregoing, as soon as the engine is started, water pump 11 is driven to rotate such that the cooling water is forced to be circulated. In this case, because the temperature of the cooling water detected by the temperature detecting element 6 is low immediately after the engine start, a signal for closing the valve unit 5 is issued thereto from said ECU 8, the motor (not shown) for controlling a butterfly valve opening angle causes the valve to be closed controlled to stay at a closed state.
Therefore, almost all of the cooling water from the engine 1 is circulated through the bypass 3c to reduce the radiation of the cooling water at the radiator.
Then, when the engine 1 is heated to raise the temperature of the cooling water, a valve open command is issued from the ECU 8 to the valve unit 5 in accordance with the cooling water temperature detected by the temperature detecting element 6 to open the butterfly valve.
Therefore, the cooling water is circulated to the radiator 2 in accordance with the extent of the valve opening where the fan unit 12 performs forced air cooling. The cooling water thus caused to circulate through the radiator 2 mixes with the cooling water which circulate through the bypass 3c and flows through the passages c of the engine 1 to cool the same.
In the cooling system, the engine is cooled by the mixture of the cooling water cooled by the radiator and the cooling water which circulates the bypass while the valve unit is operated to open and close in accordance with the information on the temperature from the temperature detecting element in the form of a thermister provided at a portion where the water from the radiator side and the bypass side meet to mix.
Then, the fan motor 12b in the fan unit 12 as a means for performing a forced air cooling is also subjected to an intermittent on- and-off control by use of the parameters based on the temperature of the cooling water, the,engine operation or the like to coordinate the temperature control of the engine in a predetermined range.
In this connection, the thus described control of the cooling operation includes a control of the valve opening by ECU after the temperature detecting element detects the temperature variation of the mixture (hereinafter referred to as Tmix) of the cooling water from the radiator side and the cooling water from the bypss side and that of an intermittent forced air cooling by means of the fan unit 12.
Therefore, when the fan unit 12 starts or stops particularly in the case of the idle running of a car, the variation of the radiation effect is so sharp that it is extremely difficult to perform the temperature control of the cooling water.
FIG. 14 shows on e ex ample of this state, in which the temperature of said Tmix rises and lowers sharply with a substantial range of .+-..alpha. in accordance with the start and stop (in FIG. 14, shown by ON and OFF) of the fan unit 12.
In general, the engine is operated to accomplish fuel economy by driving at a high temperature not to an extent to overheat while the generation of poisonous gases can be suppressed to a certain degree.
However , there remains a technical problem in the case of a substantial hunting as described in the foregoing that it cannot help but to set said Tmix at a substantially low level in order to avoid the worst situation such as the engine reaching the state of overheating, thus resulting in an unfavorable fuel consumption.